update_engine: Test update_engine printouts

These tests are added to enforce sensitive variables stay invariant
with no room or future mistakes to occur again on breaking autotest
and cros flash process.

BUG=chromium:871340
TEST=FEATURES="test" emerge-$BOARD update_engine update_engine-client
TEST=/usr/bin/update_engine_client --status
TEST=cros flash $TEST_IP ../build/image/... # works

Change-Id: Ibcce5c1dee56cf5bca201a86a143a87b033605bc
Reviewed-on: https://chromium-review.googlesource.com/c/aosp/platform/system/update_engine/+/1732410
Tested-by: Jae Hoon Kim <kimjae@chromium.org>
Auto-Submit: Jae Hoon Kim <kimjae@chromium.org>
Reviewed-by: Amin Hassani <ahassani@chromium.org>
Commit-Queue: Jae Hoon Kim <kimjae@chromium.org>
diff --git a/BUILD.gn b/BUILD.gn
index 5e76bfb..5f5aa54 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -537,6 +537,7 @@
       "update_manager/update_time_restrictions_policy_impl_unittest.cc",
       "update_manager/variable_unittest.cc",
       "update_manager/weekly_time_unittest.cc",
+      "update_status_utils_unittest.cc",
     ]
 
     # //common-mk:test should be on the top.